In humans, the skin cell turnover cycle begins at the basal layer of the dermis, where new skin cells are generated. The dermis is the mid-layer of the skin which contains blood vessels, nerves, hair roots and sweat glands. The new skin cells produced by the basal layer gradually migrate upwards, toward the outer layer of the skin, the epidermis. During this migration, the cells lose their central nucleus, alter their form, and start to produce keratin that causes them to harden. Consequently, the top layer of the epidermis, the stratus corneum, comprises such keratinized skin cells that take the form of flattened discs. These flattened cells, now called corneocytes, are effectively dead and slough off about every two to four weeks. The stratum corneum acts as the body's defense against external stimuli, water, and pathogens.
However, an excess accumulation of corneocytes is a common problem that is caused by various factors such as hormonal imbalance, age, or skin disorder. Such build up of corneocytes gives a rough and dull appearance to the skin and can also lead to skin ailments such as psoriasis, Keratosis Pilaris, folliculitis, acne, comedones, and milia. The conditions are exacerbated when oil and dirt are present due to insufficient or inefficient cleansing.
Regular exfoliation procedures have been used for centuries to supplement the natural skin cell turnover cycle. Exfoliation is a process of removing dead skin cells, such as corneocytes, oil, and dirt from the skin, and can be achieved through mechanical or chemical means. The chemical methods are called chemoexfoliation or “chemical peel” and commonly utilize alpha-, beta-, or polyhydroxy acids. The acids are applied to the skin in high concentrations by a dermatologist, or in lower concentrations by the person using over-the-counter products. The chemical peel produces a controlled partial injury to the skin by stripping off superficial skin layers. During the ensuing healing period, the epidermis is regenerated, and in case of a deeper chemical peel, the restructuring of the new dermal connective tissue takes place. This results in an improved clinical appearance of the skin. However, the drawbacks of chemoexfoliation such as cost, pain, and a long recovery period, deter many people from choosing this procedure.
Another type of exfoliation is a mechanical exfoliation of the skin using abrasives. This process involves physically scrubbing the skin with an abrasive. Traditional abrasives include crushed apricot kernel, almond shells, sugar or salt crystals, pumice, and loofahs. Co-applicant, Lynn Lucka, has previously been issued a patent on exfoliating compositions incorporating corundum (Al2O3) particles (See U.S. Pat. No. 6,290,976).
Dermabrasion is one type of such mechanical procedure which involves aggressively abrading the surface of the skin with a wire brush or a diamond wheel. The procedure minimizes the appearance of scars, dark spots, sun damages, and wrinkles. Despite its effectiveness, the associated pain requires local anesthetic and/or sedation that must be administered by a qualified physician. There is also an extensive post-procedure recovery period that lasts for a number of months due to the deep injury to the skin. Moreover, side effects of dermabrasion such as localized hyperpigmentation or hypopigmentation, infection, or hypersensitivity of the skin sometimes outweigh the benefits of the procedure.
Thus, a less invasive procedure called microdermabrasion or particle skin resurfacing has gained an increasing popularity to treat conditions such as minor sun damage, fine lines and wrinkles, enlarged pores, and coarse textured skin. In a clinical setting, the microdermabrasion procedure typically involves a device that sprays microcrystals of abrasives across the skin's surface. The procedure is virtually painless and requires little or no recovery time. Combined with thorough cleansing, microdermabrasion can be an effective method of maintaining a healthy skin. However, microdermabrasion in a clinical setting is costly and regular visits to the dermatologist are inconvenient for many consumers.
As a cheaper and convenient alternative to clinical microdermabrasion treatments, many consumers turn to personal care products such as creams, liquid cleanser, and cleansing soap bars. Microdermabrasion soap bars typically contain abrasives having a particle size diameter between 100 and 120 microns such as corundum and pumice. However, abrasives of this size are not always aggressive enough to cause the desired polishing effect on areas of the skin having thick layers of stratum corneum. This is especially true when the abrasives in a personal care product are used by an untrained consumer. One solution to the problems is to use large abrasives with a mean particle size diameter from approximately 120 to approximately 220 microns. Such large abrasives provide extra abrading power capable of removing more dirt and dead cells without unnecessary irritation. The large abrasives also provide more tactile perception that the skin is being exfoliated compared to their smaller counterparts.
For a microdermabrasion soap bar to be effective, it is imperative that the large abrasives are dispersed evenly within the soap bar. Otherwise, the soap bar may disintegrate prematurely during its use. Further, uneven distribution of abrasives in a soap bar creates areas of the soap bar with a large concentration of abrasives leaving other areas with a small concentration of abrasives. This is problematic, as the concentrated areas are extremely irritating against the skin, while the small concentration areas provide virtually no abrading effect.
Notwithstanding the foregoing, it is difficult to incorporate large abrasives within a soap bar at an amount higher than about 8%, while simultaneously preserving some of the most favored characteristics of a soap bar (e.g. appearance, cleansing ability, mildness to the skin, integrity and foamability). For example, it is possible to uniformly disperse large abrasives in a soap bar by using oils alone, such as olive oil or palm oil. However, this is done at the expense of foamability and integrity of the soap bar. A microdermabrasion soap bar containing high amounts of large abrasives with oils alone, disintegrate prematurely during the manufacturing process. The foamability and integrity of a soap bar are important from a marketing perspective, as they are a measure of product quality. Generally, high lathering soap bars with a rigid structure are capable of cleaning more effectively compared to the ones with inferior foamability and integrity. To this end, it has been unexpectedly discovered that the effects oils on the foamability and the integrity of the soap bars is ameliorated by an incorporation of butters. Furthermore, the right proportions of butters and oils in a microdermabrasion soap bar composition aid in uniformly dispersing large abrasives in the soap.
The appearance of a soap bar is another important characteristic, especially from a marketing perspective. Often, consumers choose products by their appealing appearance. A light soap color is more appealing to the consumers, as it indicates cleanliness. However, many soap products on the market that utilize natural abrasives are dark in color—a characteristic not desired in an at-home soap product. In addition, it has been found that incorporation of high amounts of various abrasives alters the color characteristics of the soap. In an effort to solve this problem, it has been unexpectedly found that using a large amount of magnesium oxide crystals in a soap does not darken the color of the soap. The soap containing such magnesium oxide particles appears white or very light blue. In contrast, using a large amount of aluminum oxide crystals or pumice has been found to blacken the appearance of the soap upon incorporation.